1. Field of the Invention
The present invention relates generally to an electromagnetic manuscript input apparatus and a method thereof, and more particularly, to an electromagnetic manuscript input apparatus and a method thereof adapted for precision positioning.
2. The Prior Arts
Computers, terminals, and other similar electronic devices should be provided with suitable input apparatuses for allowing users to input instructions, data, or select menus displayed on displays. In such a way, the computer, the terminals and the electronic devices can be controlled to work. Input apparatuses are normally categorized into contact type input apparatuses and noncontact type input apparatuses. The contact type input apparatuses include keyboard, mouse, joystick, touch panel, lightpen, remote control, digitizer, while the noncontact type input apparatuses include voice input device.
A digitizer or an electromagnetic white board should be facilitated by an electromagnetic pen for operation. In operation, the electromagnetic pen approaches or touches the digitizer, in accordance with a cursor or an image displayed on the display apparatus, to select a function menu, handwrite characters or draw a diagram. The electromagnetic pen is a very convenient input apparatus. Currently, the electromagnetic pen, and particularly the handwriting and drawing function thereof, has become widely employed in a variety of electronic products, such as computers, terminals, mobile phones, handheld digital secretaries, and touch panels.
An electromagnetic pen is a pen shaped input apparatus, including a winding, a capacitor, and a circuit board. The electromagnetic pen is capable of emitting electromagnetic waves. An electromagnetic pen may be either an active type, or a passive type. An active type electromagnetic pen includes a power supply, and a passive type electromagnetic pen does not include a power supply. The power supply of the active type electromagnetic pen is usually a battery. The passive type electromagnetic pen usually obtains power from the electromagnetic waves emitted by the digitizer, in which the electromagnetic pen has to obtain power by inducing the electromagnetic waves emitted from the digitizer.
Referring to FIG. 1, there is shown a functional block diagram illustrating a conventional electromagnetic manuscript input apparatus. The conventional electromagnetic manuscript input apparatus includes an electromagnetic pen 10 and a digitizer 20. The electromagnetic pen 10 includes a winding, a capacitor, and a circuit board (not shown in the drawing), and is capable of emitting electromagnetic waves. The digitizer 20 includes a plurality of X windings, a plurality of Y windings, an X scanning circuit 22, a Y scanning circuit 23, a signal detection circuit 24, a scan driver 26, an analog to digital converter (ADC) 28, and a coordinate controller 29, for generating a coordinate output signal 32 and transmitting the same to a posterior stage processing device, e.g., a computer, or a transmission interface such as a universal serial bus (USB) interface.
Reference numerals X1, X2, X3 . . . , represent the X windings. For example, Xn represents the nth X winding. Reference numerals Y1, Y2, Y3 . . . , represent the Y windings. For example, Ym represents the mth Y winding. The X windings and the Y windings are adapted for inducing the electromagnetic waves emitted from the electromagnetic pen 10, and generating an induction potential.
The coordinate controller 29 controls all operations of the electromagnetic manuscript input apparatus. The scan driver 26 receives a control driving signal from the coordinate controller 29, and transmits a scan driving signal 25 to the X scanning circuit 22 and the Y scanning circuit 23. The X scanning circuit 22 and the Y scanning circuit 23 drive a plurality of X windings and a plurality of Y windings, respectively. When an X winding or a Y winding is driven, an induction potential of the X winding or the Y winding is detected by the signal detection circuit 24. Correspondingly, the posterior stage ADC 28 generates a digital signal, and transmits the digital signal to the coordinate controller 29. The coordinate controller 29 receives and processes the digital signal (e.g., compare the digital signal with a noise threshold, or compare values of adjacent windings) so as to determine a maximum value and obtain a correct induction potential value. Then, the coordinate controller 29 repeats the foregoing steps, so as to obtain induction potential values of all of the X windings and the Y windings. One of the X windings having the maximum induction potential value represents an X coordinate to which the electromagnetic pen most approaches. Similarly, one of the Y windings having the maximum induction potential value represents a Y coordinate to which the electromagnetic pen most approaches. Precision coordinate values are usually obtained by calculations according to different algorithms. Generally, interpolation algorithms, such as first order approximation or a second order parabolic approximation, are often employed in conventional calculation methods.
Referring to FIG. 2, it is a schematic diagram illustrating an electromagnetic field of the electromagnetic pen 10. When the electromagnetic pen 10 defines a tilt angle with the digitizer 20, the tilt angle between the electromagnetic pen 10 and the digitizer 20 may generate a bias to the induction potential which should be further considered. As shown in FIG. 2, a larger tilt angle (θ) indicates that the winding immediately adjacent to the tilt angle (θ) generates a larger induction potential. As such, the bias caused by the tilt angle (θ) should be compensated or regulated.
Referring to FIG. 3, it illustrates an induction potential distribution of the electromagnetic pen relative to the digitizer. As shown in FIG. 3, the curves are not bilateral symmetrical. This indicates that the electromagnetic pen 10 is tilted. An X winding XP0 most adjacent to the electromagnetic pen 10 has an induction potential having a maximum peak value VP0, and a limit value (VPR, VPL) at a right side XPR and a left side XPL respectively. Further, two immediately adjacent windings (XP+, XP−) of the XPO winding have corresponding induction potentials (VP+, XP−), respectively. Referring to FIG. 4, it illustrates an induction potential distribution of an antenna winding of the digitizer, in which the slashed filled columns represent induction potentials of the X windings, while the blank columns represent that there is no X winding. Comparing with FIG. 3, FIG. 4 is simplified for more clearly depicting the coordinate positioning method of the conventional technologies, in which same numerals represent similar matters.
According to the first order approximation of the conventional technology, the coordinates of the electromagnetic pen 10 can be obtained by an interpolation algorithm. For example, the X coordinate of the electromagnetic pen 10 can be obtained from positions the windings XP0, XPR, XPL, XP+, XP−, and their corresponding induction potentials VP0, VPR, VPL, VP+, VP−, facilitated by a memory (e.g., a ROM) recording regulation values. Similarly, the Y coordinate of the electromagnetic pen 10 can also be obtained. A correct X coordinate can be obtained according to equation (1) as below:D=Sx*T+Q/G+H(f)   (1),in which D represents the correct X coordinate, Sx represents a serial number of the wiring having the maximum induction potential, T represents a coordinate value represented by a space between wirings (for the purpose of simplification, the wirings are uniformly-spaced hereby), G represents a constant, Q represents parameters related to the induction potentials VP0, VPR, VPL, f represents parameters related to the induction potentials VPR, VPL, and H(f) represents regulation values related to f. Further,Q=(VP0−VP+)/(VP0−VP−), VP+≧VP−; orQ=(VP0−VP−)/(VP0−VP+), VP+<VP−, while the regulation values of H(f) are recorded in the memory.
According to the second order parabolic approximation of the conventional technology, the coordinates of the electromagnetic pen 10 are obtained by a second order approximation interpolation algorithm. For example, the wiring positions XP0, XPR, XPL and their corresponding induction potentials VP0, VPR, and VPL are accorded for calculating the X coordinate of the electromagnetic pen 10 by an equation (2) as:VPL=a*(XPL−D)2+b VP0=a*(XP0−D)2+b VPR=a*(XPR−D)2+b   (2).Solving the equation (2), it can be obtained as:D=XPL+T/2*{(3*VPL−4*VP0+VPR)/(VPL−2*VP0+VPR)}
The conventional first order approximation interpolation has some disadvantages. For example, the induction potentials of the first order approximation interpolation are similar to a Gauss distribution, thus having a large error, and requiring a memory recording regulation values to provide compensation thereto. However, a system having more windings requires a larger memory, and therefore the hardware cost and complexity are increased correspondingly. This may even impair the reliability of the product. Further, mutual inductions between adjacent windings may also lower the precision of the method.
The conventional second order approximation interpolation also has disadvantages. For example, the induction potentials of the second order approximation interpolation are similar to a Gauss distribution, thus also having a large error. Therefore, the layout of the adjacent windings is restricted. For example, the space between the adjacent windings should be lowered, and the electromagnetic pen is restricted from being too close to the windings, for compensating the large error.
As such, it is very much desired to provide an apparatus and a method for accurately positioning the coordinate positions of the electromagnetic pen, for satisfying the higher system requirement for accuracy, and decreasing the complexity of the hardware design, and further improving the reliability of the product.